A Thermally-Driven Heat Pump Having a Heat Exchanger Located Between Displacers

ABSTRACT

A thermally driven heat pump is disclosed in which at least most of the warm heat exchanger is disposed within the cylinder between the hot and cold displacers. Such an arrangement is not suitable for a prior art heat pump in which movement of the displacers is based on a crank because it would lead to too much dead volume in the system. However, with mechatronically-controlled displacers in which the displacers are independently controlled, the displacers can reciprocate up to the heat exchanger. Such a configuration reduces dead volume compared to prior art Vuilleumier heat pumps in which the warm exchanger occupies a portion of an annular space between the cylinder in which the displacers move.

TECHNICAL FIELD

The present disclosure relates to arrangement of a heat exchanger in a thermally-driven heat pump.

BACKGROUND ART

A prior art Vuilleumier heat pump 5 is shown in FIG. 1. A hot displacer 1 and a cold displacer 2 are driven by a crank 4. In FIG. 2, the upper end of cold displacer 2 and the lower end of hot displacer 1 are shown plotted in FIG. 2, the two are out of phase by 90°. The paths of the two displacers overlap in the middle region of the cylinder in which the displacers reciprocate.

A thermally-driven heat pump in which the displacers are mechatronically actuated is disclosed in commonly-assigned patent application PCT/US13/36101 filed 11 Apr. 2013. The displacers are independently actuated such that one displacer may be held stationary while the other moves. In the heat pump disclosed in PCT/US13/36101, neither displacer reciprocates into the stroke of the other displacer, i.e., no overlap over in space of the two displacers. This is in contrast with the movement shown in FIG. 2 for a crank-driven Vuilleumier heat pump in which the displacers overlap in space, but not in time to prevent the displacers from colliding. A heat pump with independently-actuated displacers, such as disclosed in the PCT/US13/36101 application, presents opportunities not available in heat pumps in which the displacer movement is constrained by crank geometry.

DISCLOSURE

To exploit an opportunity provided by independent displacer operation over prior Vuilleumier heat pumps associated with crank movement, a heat pump is disclosed that includes a housing having: a hot cap, a cold cap, a hot cylinder portion proximate the hot cap, and a cold cylinder portion proximate the cold cap. The heat pump includes a cold displacer disposed within the cold cylinder portion, a hot displacer disposed within the hot cylinder portion, a post coupled to the cold cap and extending toward the hot cap along a centerline of the cold cylinder portion, and a substantially disk-shaped warm heat exchanger. The warm heat exchanger is located between the hot and cold displacers. An opening is defined in the warm heat exchanger to accommodate the post. A diameter of the opening in the warm heat exchanger is less than a diameter of the cold displacer. The warm heat exchanger is housed within a warm heat exchanger cylinder portion. In some embodiments, the hot cylinder portion, the cold cylinder portion, and the warm heat exchanger cylinder portion are of the same diameter.

The warm heat exchanger has an inlet that pierces the warm heat exchanger cylinder portion and an outlet that pierces the warm heat exchanger cylinder portion.

In one embodiment, the warm heat exchanger comprises at least one tube wrapped in a spiral with adjacent turns of the spiral separated by at most a predetermined distance. A working fluid within the hot and cold cylinder portions pass through the separations between adjacent turns of the spiral in response to movement of the displacers. Alternatively, the warm heat exchanger comprises a tube-and-shell heat exchanger with a working fluid within the hot and cold cylinder portions passing between the tubes in response to movement of the displacers. Alternatively, any suitable heat exchanger configuration may be provided for the warm heat exchanger.

The heat pump may further include a hot heat exchanger located proximate the hot cap and fluidly coupled to a chamber within the hot cylinder portion, a hot regenerator having one end fluidly coupled to the hot heat exchanger and one end fluidly coupled to a chamber within the cold cylinder portion, a cold heat exchanger fluidly coupled to a cold chamber within the cold cylinder portion, and a cold regenerator having one end fluidly coupled to the cold heat exchanger and one end fluidly coupled to a hot warm chamber within the hot cylinder portion.

The hot displacer reciprocation is limited by the hot cap and the warm heat exchanger. The cold displacer reciprocation is limited by the cold cap and the warm heat exchanger.

The heat pump may further include a hot heat exchanger proximate the hot cap and fluidly coupled to a hot chamber within the hot cylinder portion; a cold heat exchanger fluidly coupled to a cold chamber within the cold cylinder portion; an annular-shaped hot regenerator arranged outside the hot cylinder portion; and an annular-shaped cold regenerator arranged outside the cold cylinder portion. A first end of the hot regenerator is fluidly coupled to the hot heat exchanger and a second end of the hot regenerator is fluidly coupled to a cold warm chamber within the cold cylinder portion. A first end of the cold regenerator is fluidly coupled to the cold heat exchanger and a second end of the cold regenerator is fluidly coupled to a hot warm chamber within the hot cylinder portion.

The hot chamber is delimited by the hot cap, the hot cylinder portion, and the hot displacer. The cold chamber is delimited by the cold cap, the cold cylinder portion, and the cold displacer. The hot warm chamber is delimited by the warm heat exchanger, the hot cylinder portion, and the hot displacer. The cold warm chamber is delimited by the warm heat exchanger, the cold cylinder portion, and the cold displacer.

Also disclosed is a heat pump that includes a heat pump housing with: a hot cap, a cold cap, a hot cylinder portion near the hot cap, and a cold cylinder portion near the cold cap. The heat pump has a cold displacer disposed within the cold cylinder portion, a hot displacer disposed within the hot cylinder portion, and a substantially disk-shaped warm heat exchanger between the hot cylinder portion and the cold cylinder portion. The cold displacer reciprocates between the warm heat exchanger and the cold cap; and the hot displacer reciprocates between the warm heat exchanger and the hot cap.

The heat pump has a post coupled to the cold cap and extending toward the hot cap along a centerline of the cold cylinder portion. An opening is defined in the warm heat exchanger to accommodate the post. A diameter of the opening in the warm heat exchanger is less than a diameter of the cold displacer.

The heat pump further includes: a hot heat exchanger located proximate the hot cap and fluidly coupled to the hot cylinder portion, a hot regenerator having one end fluidly coupled to the hot heat exchanger and one end fluidly coupled to the cold cylinder portion, a cold heat exchanger fluidly coupled to the cold cylinder portion, and a cold regenerator having one end fluidly coupled to the cold heat exchanger and one end fluidly coupled to the hot cylinder portion.

The heat pump may include an annularly-shaped hot regenerator arranged outside the hot cylinder portion, an annularly-shaped cold regenerator arranged outside the cold cylinder portion, a hot chamber delimited by the hot cylinder portion, the hot displacer, and the hot cap, a hot warm chamber delimited by the hot cylinder portion, the hot displacer, and the warm heat exchanger, a cold warm chamber delimited by the cold cylinder portion, the cold displacer, and the warm heat exchanger, a cold chamber delimited by the cold cylinder portion, the cold displacer, and the cold cap, a hot heat exchanger fluidly coupled to the hot chamber and to the hot regenerator, and a cold heat exchanger fluidly coupled to the cold chamber and to the cold regenerator. The hot regenerator is fluidly coupled to the hot heat exchanger and the cold warm chamber. The cold regenerator is fluidly coupled to the cold heat exchanger and the hot warm chamber.

In some embodiments, the heat pump also has a hot heat exchanger disposed in the hot cap and a cold heat exchanger annularly arranged around the cold cylinder portion.

According to an embodiment of the present disclosure, a heat pump has a housing having a hot cap on one end of the housing and a cold cap on the other end of the housing, a cylinder within the housing, a substantially disk-shaped warm heat exchanger disposed within the housing and roughly centrally located between the hot cap and the cold cap, a hot displacer disposed in a portion of the cylinder between the warm heat exchanger and the hot cap, and a cold displacer disposed in a portion of the cylinder between the warm heat exchanger and the cold cap. The cylinder has a hot cylinder portion and a cold cylinder portion. A hot chamber is delimited by the hot cap, the hot cylinder portion, and the hot displacer. A cold chamber is delimited by the cold cap, the cold cylinder portion, and the cold displacer. A hot warm chamber is delimited by the warm heat exchanger, the hot cylinder portion, and the hot displacer. A cold warm chamber is delimited by the warm heat exchanger, the cold cylinder portion, and the cold displacer. The heat pump includes: a hot heat exchanger proximate fluidly coupled to the hot chamber, a cold heat exchanger fluidly coupled to the cold chamber, a hot regenerator, and a cold regenerator. A first end of the hot regenerator is fluidly coupled to the hot heat exchanger. A second end of the hot regenerator is fluidly coupled to a cold warm chamber. A first end of the cold regenerator is fluidly coupled to the cold heat exchanger. A second end of the cold regenerator is fluidly coupled to a hot warm chamber.

In some embodiments, the hot regenerator is annularly arranged outside the cylinder near the hot cap and the cold regenerator is annularly arranged outside the cylinder near the cold cap.

In heat pumps in which the displacers are driven by a crank arrangement, a warm heat exchanger cannot be placed within the cylinder unless the displacers were to be separated so that they do not overlap the same space. Such an arrangement would yield too much dead volume and would seriously impair thermal efficiency. The mechatronically-driven heat pump allows for the warm heat exchanger to be located within the cylinder without such a large dead volume. The gases in the cylinder readily flow over the warm heat exchanger compared with the prior-art configuration where the warm heat exchanger was in an annular volume outside the cylinder.

An advantage of the disclosed configuration is that the warm heat exchanger is more easily manufactured compared to a heat exchanger that resides in an annular volume. Another advantage of embodiments in which recuperators are disposed in the passages is that the recuperators are more easily formed in a circular or other simple cross-sectional shape compared with an annulus. Yet another advantage in some alternatives is a reduction in dead volume by obviating passages to and from the warm heat exchanger.

Vuilleumier heat pump 5 in FIG. 1 has four heat exchangers: a hot heat exchanger 6, a warm-hot heat exchanger 7, a warm-cold heat exchanger 8, and a cold heat exchanger 9. When hot displacer 1 moves downward and cold displacer 2 is mostly stationary (moving at its slowest near reversal at its lower position), or moving minimally, gases between displacers 1 and 2 are pushed through warm-hot heat exchanger 7 into a hot chamber (volume in cylinder above hot displacer 1). When cold displacer 2 moves upward and hot displacer 1 is mostly stationary (moving at its slowest near reversal at its upper position) gases between displacers 1 and 2 are pushed through warm-cold heat exchanger 8 through a regenerator and a cold chamber (volume in cylinder below cold displacer 2). There are times in the cycle in which gases are pulled into the space between the displacers from warm-hot displacer 7 and other times from warm-cold displacer 8. This present inefficiencies in there being more dead space than if a single heat exchanger could be used, simply the fact that there are two heat exchangers and the cost and complication, and the extra plumbing for the two heat exchangers. Yet other advantages according to embodiments of the present disclosure include: a single warm heat exchanger and the lack of plumbing from the space between the displacers to the warm heat exchanger. Instead, the gases flow directly from one side of the single warm heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a prior art Vuilleumier heat pump in which displacers are crank driven;

FIG. 2 is an illustration of displacer movement of the crank-driven displacers of FIG. 1;

FIG. 3 is a heat pump with mechatronically-actuated displacers;

FIGS. 4 and 16 are illustrations of a heat pump according to embodiments of the present disclosure;

FIGS. 5-15 are illustrations of the heat pump of FIG. 4 in a range of displacer positions;

FIGS. 17 and 18 are plan views of warm heat exchanger embodiments; and

FIG. 19 is an illustration of a heat pump according to an embodiment of the disclosure.

DETAILED DESCRIPTION

As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.

A thermally-driven heat pump 300 has a housing 302 which has a hot cap 304 on each end is shown in FIG. 3. Inside housing 302 is a cylinder 306. In the annular space between housing 302 and cylinder 306, a hot regenerator 332, a warm heat exchanger 334, a cold regenerator 336, and a cold heat exchanger 338 are arranged. A hot displacer 312 and a cold displacer 314 are disposed within cylinder 306 and delimit hot chamber 320, warm chamber 322, and cold chamber 326. A post 318 is coupled to cold cap 302. Displacers 312 and 314 reciprocate within cylinder 306 under control by an ECU 340. Displacers 312 and 314 have springs (not shown) that cause them to oscillate between upper and lower positions, respectively. Also not shown are the electromagnets and ferromagnetic plates associated with displacers 312 and 314. ECU 340 provides a signal to the electromagnets to attract the ferromagnetic plates to grab the displacer in one of its extreme positions. The electromagnet can hold its associated displacer until ECU 340 commands the electromagnet to de-energize to allow the displacer to act under spring control to travel to its other extreme position. More detail of mechatronic control of the displacers is found in: PCT/US13/36101 filed 11 Apr. 2013.

Continuing to refer to FIG. 3, an energy source (not shown) provides energy to a working fluid within housing 302 via a hot heat exchanger 330. When hot displacer 312 moves upward, gases flow from hot chamber 320 into hot heat exchanger 330 into hot regenerator 332 into warm heat exchanger 334 through openings 344 in cylinder 306 into the into warm chamber 322 and in the reverse order upon hot displacer 312 moving downward. Upon cold displacer 314 moving downward, the working fluid in cold chamber 326 moves through openings 342 in cylinder 316 into cold heat exchanger 338, into cold regenerator 336, into hot heat exchanger 334 into warm chamber 332 via openings 344 in cylinder 306 and in reverse order upon cold displacer 314 moving upward. Heat exchangers 334 and 338 have two fluids exchanging energy: the working fluid and a second fluid, such as a liquid. In one embodiment, the heat pump is providing domestic heating and the second fluid is water that is heated within warm heat exchanger 334. Energy is extracted from a fluid provided to cold heat exchanger 338 in such an embodiment. In another embodiment, a second fluid is provided to cold heat exchanger 338 for cooling purposes. In such embodiment, energy is exhausted via another fluid provided to warm heat exchanger 334. Provisions for inlets and outlets for a fluid other than the working fluid to heat exchangers 330, 334, and 338 are not shown in FIG. 3.

One example of motion of the displacers of FIG. 3 is illustrated in FIG. 4. Curve 240 is an illustration of the movement of the bottom edge of hot displacer (312 in FIG. 3) and line 242 shows motion of the upper edge of the cold displacer (314 in FIG. 3). At time 0, the displacers are proximate each other. At time 0, the electromagnet holding the hot displacer is de-energized to allow the hot displacer to travel toward its upper position. The motion is roughly sinusoidal. At time a, the upper electromagnet is energized to grab and hold the hot displacer. From time 0 to a, the cold displacer remains stationary at its upper position. At time a, the electromagnet grabbing the cold displacer is de-energized to allow the cold displacer to travel downward. At time 2 a, the electromagnet associated with the cold displacer grabs the cold displacer. Electromagnets are energized and de-energized to complete a cycle is complete from time 0 to time 4 a and continuing on. The dwell periods of the hot and cold displacers can be lengthened to alter the cycle to meet heating or cooling demand.

In FIG. 5, an interior of a heat pump 10 having a hot displacer 12 which reciprocates within a hot cylinder portion 16 and a cold displacer 14 which reciprocates within a cold cylinder portion 17 is illustrated. The electronic controls to manage the electromagnets (not shown) are provided through post 18. Post 18 extends from cold cap 38 toward hot cap 28 along centerline 31. A hot chamber 60 is above hot displacer 12 and a hot warm chamber 62 is below hot displacer 12. A cold chamber 66 is below cold displacer 14 and a cold warm chamber 64 is above cold displacer 14. A hot heat exchanger 20 is proximate a hot cap 28 of heat pump 10. Hot heat exchanger 20 may, in some embodiments, be in contact with a burner. Or, in other embodiments, another energy source, such as a solar collector is used. A warm heat exchanger 40 is within a warm heat exchanger cylinder portion 15 which is located between hot cylinder portion 16 and cold cylinder portion 17. Warm heat exchanger 40 is substantially in a disk shape, although with an opening in the center to accommodate post 18. A fluid passes inside the tubes of warm heat exchanger 40 with an inlet 42 and an exit 44. The working fluid within heat pump 10 passes by warm heat exchanger 40 upon movement of displacers 12 and 14. Energy is exchanged with a fluid provided to warm heat exchanger through inlet 42. A cold heat exchanger 30 is proximate a cold cap 38 of heat pump 10. A fluid passes inside the tubes of cold heat exchanger 30 with an inlet 32 and an outlet 34. The working fluid passes on the outside of the tubes of cold heat exchanger 30 with the gases flowing from cold chamber 66 to passage 36 into a cold displacer 54, into a passage 56 and exits hot warm chamber 62, when displacer 14 moves downward; and in reverse when displacer 14 moves upward. A hot regenerator 50 is located outside of cylinder 16 in passages 26 and 52. When hot displacer 12 moves upward, gases in hot chamber 60 flows on the outer surface of heat exchanger 20 into passage 26 through hot regenerator 50 through passage 52 and exits into lower warm exchanger 64.

In the embodiment in FIG. 5, cylinders 15, 16, and 17 are the same size. Alternatively, one of cylinders 16 and 17 has greater diameter than the other cylinder.

Movement of the displacers of FIG. 5 is shown in FIG. 6. Movement of hot displacer 12 is shown by curve 244 and movement of cold displacer is shown by curve 246. The movement of the displacers, curves 240 and 242, is the same as the movement of the displacers, curves 244 and 246, as shown in FIG. 4 except that the two, in FIG. 5, are separated from each other by the height of a warm heat exchanger 250.

In FIGS. 7-15, a cycle in heat pump 10 is shown. Starting in FIG. 7, hot displacer 12 is at its lower position and cold displacer 14 is at its upper position.

In FIG. 8, hot displacer 12 is moving upward, as shown by arrow 98. Movement of hot displacer 12 causes gas 102 in hot chamber 60 to pass through heat exchanger 20 into passage 26, as shown by arrow 104, through hot generator 50 into passage 52, as shown by arrow 106, and through warm exchanger 40 into hot warm chamber 62, as shown by arrow 108.

In FIG. 9, hot displacer 12 has reached its upper position and cold displacer 14 is still in its upper position.

In FIG. 10, cold displacer 14 is moving downwards, as indicated by arrow 120. Gas is pushed out of cold chamber 66, as shown by arrow 122, into cold heat exchanger 30 into passage 36, as shown by arrow 124, into cold regenerator 54 into passages 56, as shown by arrow 126, into hot warm chamber 62, through warm heat exchanger 40, as illustrated by arrow 128, and finally into cold warm chamber 64.

In FIG. 11, cold displacer has reached is lower position and hot displacer 12 is still in it upper position.

In FIG. 12, cold displacer 12 moves downwardly, as indicated by arrow 140. Gas is pushed out of hot warm chamber 62 through warm heat exchanger 40, as indicated by arrow 142, into passage 52, as indicated by arrow 144, into cold regenerator 50, into passage 26, as indicated by arrow 146, into hot heat exchanger 20, and into hot chamber 60, as indicated by arrow 148. In FIG. 13, hot displacer 14 reaches its lower position and cold displacer 12 remains at its upper position.

In FIG. 14, cold displacer 14 moves upwardly as indicated by arrow 160. Gas from upper warm chamber 64 is forced through warm heat exchanger 40, as indicated by arrow 162, into passage 56, as indicated by arrow 164, into cold regenerator 54 into passage 36, as indicated by arrow 166 through cold heat exchanger 30 into cold chamber 66, as indicated by arrow 168.

In FIG. 15, cold displacer 14 has achieved it upper position while hot displacer remains in its lower position. The cycle is completed as the position of the displacers in FIG. 15 is the same as the start position shown in FIG. 5.

The description of the gas movement implies that the gases make a complete loop. However, the gases move in the path described, but gases starting on one side of the displacer do not make the complete path to the other side of the displacer, but instead make travel through part of the loop.

An alternative heat pump 100 configuration is illustrated in FIG. 16 in which regenerators are integral with the housing. The configuration in FIG. 16 shows hot regenerator 70 annularly arranged outside of cylinder 16 and cold regenerator 74 annularly arrangement outside of cylinder 17. Also shown in heat pump 100 is a tube and shell heat exchanger 90. An inlet 92 allows a liquid, as an example, to travel through the shell of heat exchanger 90. The fluid exits at 94. The working fluid within heat pump 100 passes within the tubes of heat exchanger 90. In FIG. 16, a cold heat exchanger 31 is annularly arranged around cylinder 17. Cold heat exchanger 31 is fluidly coupled to cold regenerator 74 and to cold chamber 66. The other fluid provided to cold heat exchanger 31 has an inlet 33 and an outlet 35.

A view down the cylinder of the two warm heat exchanger alternatives previously illustrated is shown in FIGS. 17 and 18. In FIG. 17, a spiral heat exchanger 150 similar to that illustrated in FIGS. 4-15 is shown within a cylinder portion 158. Due to the reversal in the center of the spiral, both an inlet 152 and an outlet 154 are on the periphery of the spiral. An opening 156 is provided through spiral heat exchanger 150 to accommodate a post that carries electrical conductors (element 18 shown in FIG. 4).

A shell-and-tube heat exchanger 160 similar to that illustrated in FIG. 16 is shown in FIG. 18. Heat exchanger 160 is contained within a cylinder 168. An opening 166 is provided through spiral heat exchanger 150 to accommodate the post.

In the embodiment of heat pump 200 in FIG. 19, regenerators 250 and 254 are placed along cylinder wall 220 in which displacers 12 and 14 reciprocate. A heat exchanger 240 is located between displacers 12 and 14. An opening through cylinder wall 220 fluidly connects hot regenerator 250 with the chamber 62, but on the lower side of heat exchanger 240. In regards to cold regenerator 254, there is an opening in cylinder wall 220 to fluidly connect cold regenerator 254 with chamber 62, on the upper side of heat exchanger 240. Water or other fluid to be heated is provided to heat exchanger 240 through inlet 192 that goes through hot regenerator 250 and exits through outlet 194, which goes through cold regenerator 254. In other embodiments, the lower portion of the space for hot regenerator 250 and the upper portion of the space for cold regenerator 254 is actually an extension of heat exchanger 240. In such embodiment, part of heat exchanger 240 is within cylinder wall 220 and part of heat exchanger 240 is outside cylinder wall 220.

While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications. 

1. A heat pump, comprising: a heat pump housing having: a hot cap, a cold cap, a hot cylinder portion proximate the hot cap, and a cold cylinder portion proximate the cold cap; a cold displacer disposed within the cold cylinder portion; a hot displacer disposed within the hot cylinder portion; and a substantially disk-shaped warm heat exchanger between the hot cylinder portion and the cold cylinder portion wherein: the cold displacer reciprocates between the warm heat exchanger and the cold cap; and the hot displacer reciprocates between the warm heat exchanger and the hot cap.
 2. The heat pump of claim 1, further comprising: a post coupled to the cold cap and extending toward the hot cap along a centerline of the cold cylinder portion wherein: an opening is defined in the warm heat exchanger to accommodate the post; and a diameter of the opening in the warm heat exchanger is less than a diameter of the cold displacer.
 3. The heat pump of claim 1, further comprising: a hot heat exchanger located proximate the hot cap and fluidly coupled to the hot cylinder portion; and a hot regenerator having one end fluidly coupled to the hot heat exchanger and one end fluidly coupled to the cold cylinder portion.
 4. The heat pump of claim 1, further comprising: a cold heat exchanger fluidly coupled to the cold cylinder portion; and a cold regenerator having one end fluidly coupled to the cold heat exchanger and one end fluidly coupled to the hot cylinder portion.
 5. The heat pump of claim 1, further comprising: a hot regenerator arranged outside the hot cylinder portion; and a cold regenerator arranged outside the cold cylinder portion.
 6. The heat pump of claim 5, further comprising: a hot chamber delimited by the hot cylinder portion, the hot displacer, and the hot cap; a hot warm chamber delimited by the hot cylinder portion, the hot displacer, and the warm heat exchanger; a cold warm chamber delimited by the cold cylinder portion, the cold displacer, and the warm heat exchanger; a cold chamber delimited by the cold cylinder portion, the cold displacer, and the cold cap; and a hot heat exchanger fluidly coupled to the hot chamber and to the hot regenerator; a cold heat exchanger fluidly coupled to the cold chamber and to the cold regenerator, wherein: the hot regenerator is fluidly coupled to the hot heat exchanger and the cold warm chamber; and the cold regenerator is fluidly coupled to the cold heat exchanger and the hot warm chamber.
 7. The heat pump of claim 1, further comprising: a hot heat exchanger disposed in the hot cap; and a cold heat exchanger annularly arranged around the cold cylinder portion.
 8. The heat pump of claim 1 wherein: the warm heat exchanger comprises at least one tube wrapped in a spiral; adjacent turns of the spiral are separated by at most a predetermined distance; and a working fluid within the hot and cold cylinder portions pass through the separations between adjacent turns of the spiral in response to movement of the displacers.
 9. The heat pump of claim 1, further comprising: a hot heat exchanger proximate the hot cap and fluidly coupled to a hot chamber within the hot cylinder portion; a cold heat exchanger fluidly coupled to a cold chamber within the cold cylinder portion; an annular-shaped hot regenerator arranged outside the hot cylinder portion; and an annular-shaped cold regenerator arranged outside the cold cylinder portion wherein: a first end of the hot regenerator is fluidly coupled to the hot heat exchanger; a second end of the hot regenerator is fluidly coupled to a cold warm chamber within the cold cylinder portion; a first end of the cold regenerator is fluidly coupled to the cold heat exchanger; and a second end of the cold regenerator is fluidly coupled to a hot warm chamber within the hot cylinder portion.
 10. The heat pump of claim 1 wherein the warm heat exchanger is housed within a warm heat exchanger cylinder portion; and the hot cylinder portion, the cold cylinder portion, and the warm heat exchanger cylinder portion are of the same diameter.
 11. The heat pump of claim 1 wherein the warm heat exchanger is housed within a warm heat exchanger portion; and the warm heat exchanger has an inlet that pierces the warm heat exchanger cylinder portion and an outlet that pierces the warm heat exchanger cylinder portion.
 12. A heat pump, comprising: a housing having a hot cap on one end of the housing and a cold cap on the other end of the housing; a cylinder within the housing; a substantially disk-shaped warm heat exchanger disposed within the housing and roughly centrally located between the hot cap and the cold cap; a hot displacer disposed in a portion of the cylinder between the warm heat exchanger and the hot cap; and a cold displacer disposed in a portion of the cylinder between the warm heat exchanger and the cold cap.
 13. The heat pump of claim 12 wherein the cylinder has a hot cylinder portion and a cold cylinder portion, the heat pump further comprising: a hot chamber delimited by the hot cap, the hot cylinder portion, and the hot displacer; a cold chamber delimited by the cold cap, the cold cylinder portion, and the cold displacer; a hot warm chamber delimited by the warm heat exchanger, the hot cylinder portion, and the hot displacer; a cold warm chamber delimited by the warm heat exchanger, the cold cylinder portion, and the cold displacer; a hot heat exchanger proximate fluidly coupled to the hot chamber; a cold heat exchanger fluidly coupled to the cold chamber; a hot regenerator; and a cold regenerator, wherein: a first end of the hot regenerator is fluidly coupled to the hot heat exchanger; a second end of the hot regenerator is fluidly coupled to a cold warm chamber; a first end of the cold regenerator is fluidly coupled to the cold heat exchanger; and a second end of the cold regenerator is fluidly coupled to a hot warm chamber.
 14. The heat pump of claim 13 wherein: the hot regenerator is annularly arranged outside the cylinder near the hot cap; and the cold regenerator is annularly arranged outside the cylinder near the cold cap.
 15. A heat pump, comprising: a heat pump housing having: a hot cap, a cold cap, a hot cylinder portion proximate the hot cap, and a cold cylinder portion proximate the cold cap; a cold displacer disposed within the cold cylinder portion; a hot displacer disposed within the hot cylinder portion; and a substantially disk-shaped warm heat exchanger wherein: the warm heat exchanger is located between the hot and cold displacers.
 16. The heat pump of claim 1.5 wherein: the warm heat exchanger is housed within a warm heat exchanger cylinder portion; and the hot cylinder portion, the cold cylinder portion, and the warm heat exchanger cylinder portion are of the same diameter.
 17. The heat pump of claim 15 wherein the warm heat exchanger has an inlet that pierces the warm heat exchanger cylinder portion and an outlet that pierces the warm heat exchanger cylinder portion.
 18. The heat pump of claim 15 wherein: the warm heat exchanger comprises at least one tube wrapped in a spiral; adjacent turns of the spiral are separated by at most a predetermined distance; and a working fluid within the hot and cold cylinder portions pass through the separations between adjacent turns of the spiral in response to movement of the displacers.
 19. The heat pump of claim 15, further comprising: a hot heat exchanger located proximate the hot cap and fluidly coupled to a chamber within the hot cylinder portion; a hot regenerator having one end fluidly coupled to the hot heat exchanger and one end fluidly coupled to a chamber within the cold cylinder portion.
 20. The heat pump of claim 15, further comprising: a hot heat exchanger proximate the hot cap and fluidly coupled to a hot chamber within the hot cylinder portion; a cold heat exchanger fluidly coupled to a cold chamber within the cold cylinder portion; an annular-shaped hot regenerator arranged outside the hot cylinder portion; and an annular-shaped cold regenerator arranged outside the cold cylinder portion wherein: a first end of the hot regenerator is fluidly coupled to the hot heat exchanger; a second end of the hot regenerator is fluidly coupled to a cold warm chamber within the cold cylinder portion; a first end of the cold regenerator is fluidly coupled to the cold heat exchanger; and a second end of the cold regenerator is fluidly coupled to a hot warm chamber within the hot cylinder portion. 